Topic
Stygimoloch
About: Stygimoloch is a research topic. Over the lifetime, 4 publications have been published within this topic receiving 199 citations.
Papers
TL;DR: It is proposed that Dracorex hogwartsia, Stygimoloch spinifer and Pachycephalosaurus wyomingensis are the same taxon and represent an ontogenetic series united by shared morphology and increasing skull length.
Abstract: Background Extended neoteny and late stage allometric growth increase morphological disparity between growth stages in at least some dinosaurs. Coupled with relatively low dinosaur density in the Upper Cretaceous of North America, ontogenetic transformational representatives are often difficult to distinguish. For example, many hadrosaurids previously reported to represent relatively small lambeosaurine species were demonstrated to be juveniles of the larger taxa. Marginocephalians (pachycephalosaurids + ceratopsids) undergo comparable and extreme cranial morphological change during ontogeny. Methodology/Principal Findings Cranial histology, morphology and computer tomography reveal patterns of internal skull development that show the purported diagnostic characters for the pachycephalosaurids Dracorex hogwartsia and Stygimoloch spinifer are ontogenetically derived features. Coronal histological sections of the frontoparietal dome of an adult Pachycephalosaurus wyomingensis reveal a dense structure composed of metaplastic bone with a variety of extremely fibrous and acellular tissue. Coronal histological sections and computer tomography of a skull and frontoparietal dome of Stygimoloch spinifer reveal an open intrafrontal suture indicative of a subadult stage of development. These dinosaurs employed metaplasia to rapidly grow and change the size and shape of their horns, cranial ornaments and frontoparietal domes, resulting in extreme cranial alterations during late stages of growth. We propose that Dracorex hogwartsia, Stygimoloch spinifer and Pachycephalosaurus wyomingensis are the same taxon and represent an ontogenetic series united by shared morphology and increasing skull length. Conclusions/Significance Dracorex hogwartsia (juvenile) and Stygimoloch spinifer (subadult) are reinterpreted as younger growth stages of Pachycephalosaurus wyomingensis (adult). This synonymy reduces the number of pachycephalosaurid taxa from the Upper Cretaceous of North America and demonstrates the importance of cranial ontogeny in evaluating dinosaur diversity and taxonomy. These growth stages reflect a continuum rather than specific developmental steps defined by “known” terminal morphologies.
155 citations
TL;DR: In this paper, an end-stage juvenile Pachycephalosaurus from the Upper Cretaceous Hell Creek Formation, Montana, was used to confirm the earliest expression of squamosal nodes, parietal ornamentation, and jugal morphology in the smallest and presumably youngest individuals yet known.
Abstract: New end-stage juvenile specimens of Pachycephalosaurus from the Upper Cretaceous Hell Creek Formation, Montana, confirm the earliest expression of squamosal nodes, parietal ornamentation, and jugal morphology in the smallest and presumably youngest individuals yet known. High-resolution computed tomography of the slightly thickened, undomed parietal reveals a dense cortex, a highly cancellous interior of irregularly shaped erosion cavities, and bony trabeculae indicative of primary, fast growing bone. The parietal, with its highly ornamented septum morphology and patent sutures, is nearly identical to the holotype of ‘Dracorex hogwartsia,’ and combined with these new internal histological details, supports the alternative interpretation that ‘D. hogwartsia’ is a juvenile Pachycephalosaurus wyomingensis. The squamosal nodes grow into an array of horns and secondary nodes exemplified by the pachycephalosaurin ‘Stygimoloch spinifer’ considered in this study to be a subadult P. wyomingensis. Unlike t...
34 citations
TL;DR: A new skull of Stygimoloch spinifer from the Upper Cretaceous Hell Creek Formation of North Dakota is the most complete specimen discovered to date and confirms a suite of diagnostic characters for the species.
Abstract: A new skull of Stygimoloch spinifer (MPM 8111) from the Upper Cretaceous Hell Creek Formation of North Dakota is the most complete specimen discovered to date. It allows much of the skull and braincase of this unusual pachycephalosaurid to be described for the first time and confirms a suite of diagnostic characters for the species. The skull is long with a vaulted, transversely narrow frontoparietal dome and a robust squamosal forming a prominent posterior shelf. The shelf is ornamented by three to four large, low-angle horns and multiple clusters of smaller bony nodes. The orientation of the squamosal is preserved along an unambiguous contact with the frontoparietal suture, allowing definitive determination of the orientation of the squamosal horns. These cranial features indicate a different mode of agonistic behavior than previously suggested for Stegoceras and Pachycephalosaurus. The high, narrow dome of S. spinifer is not suited for head-butting, and the orientation of its squamosal horns a...
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2016 | 1 |
| 2009 | 1 |
| 1998 | 1 |
| 1990 | 1 |